Gardnerella is not an STI. Gardnerella vaginalis is a bacterium that lives in the vagina of many women, and that increases sharply in bacterial vaginosis. So you do not catch it from someone the way you catch chlamydia.
People still get a fright when that name appears on a result, and we understand why. A Latin bacterial name next to the word vagina reads as bad news. Here is what it actually means.
What exactly is gardnerella vaginalis?
It is a bacterium described in 1955 by Hermann Gardner and Charles Dukes, later named after Gardner. It belongs to the normal vaginal flora of a large share of women. Only when the lactobacilli decrease and gardnerella takes over alongside other species does the picture we call bacterial vaginosis appear.
In 2019 Vaneechoutte and colleagues showed that gardnerella is not one species but a group of related ones. That partly explains why one woman with gardnerella has complaints and another does not.
Presence is therefore not the same as disease. That distinction is the heart of this whole topic.
So why is gardnerella on my result?
Because some laboratory techniques report everything they find, including bacteria that belong there. A culture or a broad molecular panel can flag gardnerella without anything being wrong. The finding only gains meaning alongside your complaints and the other features of bacterial vaginosis.
| Gardnerella vaginalis | An actual STI (trichomonas, say) | |
|---|---|---|
| Part of your normal flora? | Often yes | No, never |
| Passed on through sex? | Not as classic transmission | Yes |
| Does presence mean disease? | Not necessarily | Yes |
| Treat the partner too? | Usually not | Yes, that is standard |
| In a standard STI test? | No | Yes |
The bottom row explains the confusion. Anyone taking an STI test expecting gardnerella to appear is looking in the wrong investigation.
Can you catch gardnerella from your partner?
Not the way an STI is transmitted, although sex does play a role. Research shows that a new partner, multiple partners and sex without a condom are linked to a higher chance of bacterial vaginosis. Muzny and Schwebke described in 2016 how sexual contact can shift the vaginal bacterial makeup without classic transmission taking place.
There is also animal work showing that gardnerella can trigger the picture alongside other bacteria, rather than on its own.
In practice this means your partner is usually not a source that needs treating. With a parasitic STI like trichomonas it works differently, and that difference is exactly why which of the two you have matters.
When is an STI test worthwhile then?
When you have complaints after a risk moment, because then infections that do not belong there may be involved. Chlamydia, gonorrhoea and trichomonas sometimes cause the same change in discharge as bacterial vaginosis. Gardnerella on your result does not rule those three out, because they were not looked for in the same investigation.
If you do want to know, a chlamydia, gonorrhoea and trichomonas test covers it. The RIVM publishes annually how often these STI diagnoses are made in the Netherlands.
Imagine someone told 2 weeks after a swab that gardnerella was found, assuming this explains her complaints, and never testing for the rest. If chlamydia was also present, it stays unnoticed.
I see that thinking error more than any other on this topic: one name on a result feels like a finished answer.
What you can do next
If you have complaints and there was no risk moment, your GP is the logical step for assessing bacterial vaginosis itself. If there was a risk moment, ruling out the STI side first is the level-headed order.
Read the full overview in bacterial vaginosis, thrush or trichomonas, see what each complaint means in bacterial vaginosis symptoms, and read about the STI that resembles it most in trichomonas symptoms in women.
Every blood test result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
References
- Vaneechoutte M, et al. Emended description of Gardnerella vaginalis and description of Gardnerella leopoldii, Gardnerella piotii and Gardnerella swidsinskii. International Journal of Systematic and Evolutionary Microbiology, 2019. PMID: 30648938
- Muzny CA, Schwebke JR. Pathogenesis of Bacterial Vaginosis: Discussion of Current Hypotheses. The Journal of Infectious Diseases, 2016. PMID: 27449868
- Gilbert NM, et al. Gardnerella vaginalis and Prevotella bivia Trigger Distinct and Overlapping Phenotypes in a Mouse Model of Bacterial Vaginosis. The Journal of Infectious Diseases, 2019. PMID: 30715405
- Amsel R, et al. Nonspecific vaginitis. Diagnostic criteria and microbial and epidemiologic associations. The American Journal of Medicine, 1983. PMID: 6600371
- RIVM, sexually transmitted infections in the Netherlands, annual surveillance report
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